The naphtha solvents have different applications in chemical and petrochemical industries such as solvents for extraction of vegetable oil, polymerization process and for cleanup and maintenance operations. Naphtha solvents used in food processing to extract selective ingredient from a raw material, should follow the criteria set for toxicological norms and in petrochemical process. High purity hexane is naphtha solvent in the range of 65° C. to 70° C. with aromatics, mainly benzene known as High purity hexane widely used in polymerization and food industry.
Several processes such as catalytic hydrogenation, adsorptive de-aromatization, catalytic distillation and solvent extraction have been currently followed in industry for reduction of benzene in naphtha for the production of food grade hexane.
U.S. Pat. No. 3,505,421 describes a process of hydrogenating benzene in liquid phase by means of molecular hydrogen in the presence of suspended solid catalyst. U.S. Pat. No. 5,254,763 also describes a process for selective hydrogenation of benzene using water soluble organo-metallic hydrogenation catalyst. This hydrogenation process involves hydrogen at elevated temperature and pressure. The hydrogenation process also involves the removal of sulfur before the reaction, which makes this process more expensive.
The adsorptive de-aromatization was achieved using activated carbon, alumina, and zeolite materials. U.S. Pat. No. 3,963,934 claims the separation of aromatics from process streams by use of a molecular sieve. Other U.S. Pat. Nos. 2,728,800; 2,847,485; and 2,856,444 describes the use of silica gel for adsorbing aromatics from a process stream, followed by desorption by use of a liquid hydrocarbon. U.S. Pat. No. 5,294,334 describes the process for selectively removing benzene from gasoline boiling range process streams using aluminosilicate zeolite material. The catalytic distillation for benzene removal is another method/technology.
U.S. Pat. No. 7,501,549 claims the reduction in benzene from gasoline can be achieved by feeding a gasoline fraction with an alcohol and ether to a catalytic distillation column with one reaction zone containing an alkylation catalyst. Then the C6 hydrocarbons are separated from C7+ hydrocarbons. The catalytic hydrogenation is another method for benzene removal where benzene reduction, olefin saturation and sulfur reduction occurs simultaneously.
U.S. Pat. No. 6,153,805 discloses the catalytic hydrogenation of benzene to produce cyclohexane in the presence of metal catalyst. US Patent Application 2002/24395 discloses the production of food grade hexane by hydrogenation, using Ni supported alumina catalyst. U.S. Pat. No. 4,428,829 reports the production of food grade hexane by separating aromatics and non-aromatics from heavy hydrocarbon stream by extraction process.
U.S. Pat. No. 5,668,293 discloses the process and catalyst for the production of cyclohexane by hydrogenation of benzene, comprising of two steps: a) gradually introducing the feed of benzene for hydrogenation and a hydrogen-rich gas into a reaction zone containing a cyclohexane-rich liquid and a nickel-based catalyst in colloidal suspension and recovering a gaseous phase containing cyclohexane, hydrogen and benzene; and b) introducing the gaseous phase into a reactor operating under hydrogenation conditions and containing at least one fixed bed of a solid nickel-based hydrogenation catalyst.
Indian patent applications 1224/DEL/1994 & 788/DEL/1994 discloses the separation of the aromatics and non-aromatics from naphtha and kerosene range fraction by extraction. The raffinate phase is water washed to remove the solvent carryover. The U.S. patent application 20040182750 discloses the process for removal of aromatics from petroleum streams like naphtha, kerosene and gasoil through extraction by using solvents like NMP, Sulfolane and glycol. In all the above said process, solvent is recovered by distillation.
U.S. Pat. No. 3,551,327 discloses a process for recovery of aromatics from vapour to liquid phase i.e. by extractive distillation, further it also focuses on raffinate water wash and recovery of sulfolane from water. US patent application 20040182750 discloses a process for extraction of aromatics from petroleum fraction like heavy naphtha, kerosene and gas oil. U.S. Pat. Nos. 3,942,765; 4,314,974 discloses a process for the removal of metal ions from aqueous solution by using solvent in different type of static mixer and then whole process is confined to static mixer alone. The processes for producing food grade hexane containing less than 100 ppm benzene is hydrogenation (U.S. patent application 20050224395) and adsorption (U.S. Pat. No. 4,567,315).
U.S. Pat. No. 6,048,450 discloses a process for the selective reduction in the content of light unsaturated compounds (that is to say containing at the most six carbon atoms per molecule) including benzene, in a hydrocarbon cut comprising mainly at least 5 carbon atoms per molecule, without any significant loss in the octane number, said process comprising passing said cut into a distillation zone associated with a hydrogenation reaction zone, followed by passing part of the effluent from the distillation zone comprising mainly C5-C6 hydrocarbons, that is to say containing 5 and/or 6 carbon atoms per molecule into a zone for the isomerization of paraffins in the presence of an isomerization catalyst, to obtain an isomerate containing an increased concentration of branched hydrocarbons.
US20140353216 discloses a column for consecutive extractive distillations, in particular of crude hydrocarbon mixes comprising aromatic, naphthene and paraffin hydrocarbons. It also discloses the methods for separating and recovering the components of a crude hydrocarbon mix comprising aromatic, naphthene and paraffin hydrocarbons by consecutive extractive distillations.
All the above discussed prior arts need the refineries, which are producing food grade hexane by solvent extraction process, need to put up separate unit to employ these processes which is cost intensive.
Specifications for food grade hexane with respect to benzene content are becoming stringent day by day. Refineries producing food grade hexane by solvent extraction process need to switch to alternative processes like catalytic hydrogenation and adsorption which calls for additional capital investment. Thus there is a need for a process for production of High purity hexane employing extractive distillation using solvent having similar dispersive force parameter to that of component.